消息异常处理

#import "ViewController.h"
#import <objc/runtime.h>
#import "AppDelegate.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 调用一个没有实现的方法
    [self performSelector:@selector(haha)];
}

/*处理不能识别的方法，会经历如下步骤，前一个步骤走不通的时候就会走下一个步骤*/

#if 1 //step1:决议机制，是否为该sel动态的添加一个方法实现
+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    NSString *selname = NSStringFromSelector(sel);
    if ([selname isEqualToString:@"haha"]) {
        class_addMethod(self, sel, class_getMethodImplementation([AppDelegate class], @selector(haha)), method_getTypeEncoding(class_getInstanceMethod([AppDelegate class], @selector(haha))));
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

- (void)oklala {
    NSLog(@"oklala");
}
#endif

#if 1 // step2:转发给其它的对象处理
- (id)forwardingTargetForSelector:(SEL)aSelector
{
    return [[AppDelegate alloc] init];
}
#endif

#if 1 // step3: 封装成NSInvocation对象转发处理，系统默认是调用doesNotRecognizeSelector，重写forwardInvocation:方法同时必需重写methodSignatureForSelector:(构造NSInvocation对象必需先有一个NSMethodSignature对象),
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    NSLog(@"~~~~%@", [anInvocation description]);
}  

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    NSLog(@"%@", NSStringFromSelector(aSelector));
    NSMethodSignature *sig = [NSMethodSignature signatureWithObjCTypes:"@@:"];
    return sig;
}
#endif

@end